What classifies an insect as a tick?

An insect is classified as a tick primarily due to its ability to survive for lengthy periods without food. Ticks are arachnids and not insects, and they have evolved to endure extended periods without taking a blood meal, which allows them to survive in various environmental conditions. This survival adaptation plays a crucial role in their life cycle, particularly through the various stages they undergo, including larva, nymph, and adult.

While the other options touch upon certain characteristics that may apply to some arachnids, they do not specifically define what classifies an organism as a tick. Ticks do not solely have a hard body, nor do they have a distinct 'true head' as seen in other insects. Furthermore, ticks are obligate blood-feeders, meaning that they primarily feed on the blood of animals and not on plant matter, which also separates them from classifications that pertain to herbivorous insects.